1. Field of the Invention
The present invention relates to an adhesive for fibrous materials, and more particularly to an adhesive which well adheres a polyester fibrous material to rubber and reduces a deterioration of adhesion even under a high-temperature using condition and a deterioration of strength of the polyester fibrous material.
2. Description of the Prior Art
Polyester materials typified by polyethylene terephthalate, which are a linear micromolecule having ester linkage in its main chain, retain stable properties and are less in the stress mitigation and have excellent creep characteristics and excellent stretch elastic recovery and the like as compared with nylon material or the like, so that they are very useful as a reinforcing material for rubber articles such as tire, belt, air spring, rubber hose and the like in the form of filament, yarn, cord, cable cord fabric, canvas or the like.
However, these rubber articles are generally used under a high strain and a high temperature, so that a heat particularly generated under the high strain and a surrounding heat cause a deterioration in the strength of the polyester fibrous material and a deterioration in the adhesion to rubber articles.
Recently, with the advancement of motorization, fibrous reinforcing rubber articles such as tire and the like have required a weight saving of the article itself. For this purpose, the thinning and weight saving of the article have been effected by using reinforcement materials having a thick diameter and a high strength. However, this tends to cause more heat build-up of the rubber article because the higher loading and stress are applied to each of the reinforcement materials. Moreover, large-size tires requiring a high level of durability have a trend to make the thickness of the tread portion thicker, which is required to use a polyester fibrous material having an excellent heat resistance.
An adhesive for rubber consisting mainly of a solution of polyhydric phenol-polysulfide dissolved in resorcin-formaldehyde condensate containing an excess amount of resorcin (hereinafter abridged as resorcin excess resorcin-formaldehyde condensate) has been proposed (see U.S. Pat. No. 3,705,868), which has got some good results but is particularly poor in the heat aging characteristics, and thus could not meet a recent requirement for increasing the durability in rubber articles.